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Will PETG Melt in the Sun? The Definitive Answer

PETG, also styled as PET-G, is polyethylene terephthalate glycol, a thermoplastic polyester widely used in 3D printing. It’s swiftly becoming a default choice for 3D printing, especially to create objects and builds that need to endure the various environmental elements outdoors. 

PETG won’t melt in the sun. Its melting point is 500 °F (260 °C), and the glass transition temperature is 176 °F (80 °C). Also, PETG is more resistant than other thermoplastic filaments to UV-A and UV-B radiation while being immune to the UV-C rays of the sun. 

3D printing thermoplastics, whether filaments or others, generally don’t melt in the sun due to the heat. The first effect is discoloration, and then the plastic may turn soft, brittle, and deform to an extent. This guide explains why PETG has no such vulnerabilities and can endure the sun. 

Is PETG Sun Resistant?

PETG is mildly sensitive only to the 300 nm up to 340 nm wavelengths of the ultraviolet or UV radiation in the solar spectrum, which is the transition range between UV-B and UV-A. Thus, PETG is more resistant to the sun than other plastics like PLA, ABS, and PC. 

Here are the wavelengths of the sun’s ultraviolet radiation:

  • UV-A: 315 nm to 400 nm
  • UV-B: 280 nm to 315 nm
  • UV-C: 100 nm to 280 nm

Here’s a UV sensitivity comparison of common 3D printing plastics:

3D Printing Thermoplastics (Polymers)UV Wavelength Sensitivity
PETG (Polyethylene terephthalate glycol)300 nm to 340 nm
ABS (Acrylonitrile butadiene styrene)300 nm to 390 nm
PC (Polycarbonate)280 nm to 310 nm
PP (Polypropylene)290 nm to 370 nm
Nylon (Polyamides)290 nm to 315 nm
PLA (Polylactic acid)Not UV Resistant*

*PLA absorbs 200 nm to 400 nm of UV radiation and cannot endure prolonged sun exposure.

PETG has a much smaller sensitivity range than the other polymers or thermoplastics. Only PC or polycarbonate has a shorter range, but it is entirely within the UV-B spectrum. Thus, polycarbonate suffers immense damage when exposed to the sun. 

Many thermoplastics have UV-resistant grades available these days. However, the foundation or primary material still has the most significant impact on the eventual resistance to the sun, whether it’s heat or UV radiation. So, PETG is an undisputed winner with superior attributes. 

Is PETG Good for Outdoor Use?

PETG is an excellent choice for outdoor use. The material doesn’t soften or turn brittle due to exposure to the sun’s UV rays. PETG is resistant to heat, cold, shock, and solvent. Also, it can endure natural elements, such as strong winds, rain, and snow.

PETG is rigid and stable with a negligible shrinkage of 0.2% to 0.6% when curing 3D printed objects. Also, UV-graded PETG won’t even suffer any noticeable discoloration upon prolonged outdoor use. Furthermore, PETG is durable at temperatures as low as -20 °F (-28.9 °C).

In other words, you don’t have to worry about PETG objects in almost all outdoor conditions, from scorching summer noon to freezing winter midnight and everything in between. However, the quality of your 3D printed object will certainly influence its real-world durability

Will PETG Melt in Car?

PETG won’t melt in your car unless the temperature inside the cabin somehow reaches ~176 °F (80 °C). Even then, the 3D object won’t melt but may soften a little in prolonged exposure, which could be unnoticeable on a sturdy UV-graded PETG object or build.

Thermoplastics such as polymers or polyesters have a glass transition temperature that determines if the material will turn soft when exposed to that particular degree of heat. It’s this glass transition temperature that decides whether or not a thermoplastic will soften in your car.

PETG’s glass transition temperature is higher than PLA. ABS has a better glass transition temperature than PETG, but its UV sensitivity makes it unsuitable for outdoor use or prolonged exposure to sunlight, whether inside or on a car. Thus, PETG is more suitable than PLA and ABS.

Also, PETG has no odor or taste, and it doesn’t have the hazing problem that is common in many 3D printing materials when they’re subjected to high heat during a build. Hence, PETG objects won’t cause any inconvenience in your car, even when the mercury soars in summer. 

Is PETG As Strong as ABS?

PETG is a rigid and stable thermoplastic polyester with deflection and service temperatures of 157 °F (69.4 °C) and 156 °F (68.9 °C), respectively. There are flame-retardant PETGs, too. 100% recyclable, exceptionally pliable, and UV-resistant PETG is stronger than ABS.

ABS is a strong thermoplastic, but it doesn’t endure the natural elements remotely as well as PETG. You may choose either for indoor use. However, if you need to use a 3D printed object or build outside, choosing PETG over ABS isn’t even a debate as the latter will discolor and deform. 

Is PETG Better Than PLA?

PLA isn’t UV-resistant. 3D printed PLA models will discolor in a day or two upon prolonged exposure to the sun. Also, PLAs have lower glass transition temperatures of 122 °F (50 °C) to 149 °F (65 °C), so they turn soft and brittle and deform sooner than PETG.

Neither PLA nor ABS is as resistant as PETG to the sun, its UV rays, and the natural elements like rain. The only material you could consider a worthy rival is ASA (acrylonitrile styrene acrylate or acrylic styrene-acrylonitrile). However, PETG is FDA-compliant, and ASA isn’t.

Conclusion

PETG is widely used in the healthcare sector for medical purposes and pharmaceutical packaging, the food industry for containers and trays, and in outdoor advertising, branding, and retail signages. The material has proven its endurance, durability, and utility over the years. 

The heat and UV-resistance attribute apart, PETG is available in myriad colors, including transparent and opaque. Also, PETG is waterproof, resistant to many solvents, including chemicals, and is a food-grade thermoplastic polyester, safe for all kinds of models and builds.